A magnetic tunnel junction (MTJ) element also referred to as a sensor is a key component of magnetic recording devices. There is a continuous push to increase recording density which requires the sensor to become smaller in order to meet high performance demands of new devices. There are several ways to generate sensors with a smaller CD. One is to reduce the CD by shrinking the mask dimension in the pattern that is printed into a photoresist mask layer. Subsequently, the mask pattern is transferred through a MTJ stack of layers with an etch process to produce a plurality of MTJ elements with a CD similar to that in the photoresist pattern. Secondly, once the MTJ element is defined by the pattern transfer process, a reactive ion etch (RIE) may be used to trim the sidewalls and thereby shrink the dimension of the sensor. However, both of these methods have practical limits and cannot reproducibly generate a CD less than about 50 nm which is needed in high performance recording devices.
A MTJ element may be based on a TMR effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer. In a GMR sensor, the non-magnetic spacer is typically Cu or another non-magnetic metallic layer. In a sensor, the MTJ element is formed between two shields. A MTJ stack of layers that is subsequently patterned to produce a MTJ element may be formed in a so-called bottom spin valve configuration by sequentially depositing a seed layer, an anti-ferromagnetic (AFM) pinning layer, a ferromagnetic “pinned” layer, a thin tunnel barrier layer, a ferromagnetic “free” layer, and a capping layer on a substrate. The AFM layer holds the magnetic moment of the pinned layer in a fixed direction. The free layer has a magnetization that is able to rotate and thereby establish two different magnetic states. Alternatively, the MTJ element may have a top spin valve configuration wherein a free layer is formed on a seed layer followed by sequentially forming a tunnel barrier layer, a pinned layer, AFM layer, and a capping layer, for example.
A routine search of the prior art revealed the following references. U.S. Pat. Nos. 7,438,982, 7,616,404, 7,615,292, and U.S. Patent Application 2008/0078739 all relate to the use of IBE at certain incident angles to modify a surface of a magnetic recording medium but do not teach about shaping sensor sidewalls.
U.S. Pat. No. 7,561,384 discloses a method of patterning a sensor by employing two IBE steps where the second step involves an incident angle greater than the incident angle used in the first step. The second IBE step removes redeposited material from the first IBE step. However, this reference does not address any detrimental effect the second IBE step has on the magnetic properties of sensor layers.
None of the prior art methods provide a solution for achieving a high performance sensor CD less than 50 nm in a reliable manner by trimming a sidewall of a MTJ element. Therefore, a new method is required in order to enable further advances in magnetic recording devices.